This invention relates to the inactivation of viruses in blood products. It relates more particularly to a method and apparatus for inactivating viruses in blood products through the use of high temperature short time heating (HTST) of those products.
Currently in the United States, about 3 to 4 milling people receive blood transfusions each year, averaging 3.5 units per person. As is well known, serious reactions can occur at the time of transfusion, including the transmission of blood born infection such as hepatitis, syphilis and the HIV virus. Despite the existence of tests for such infections and improved donor selection and screening procedures, each year many people acquire viral illnesses from transfusions of blood products such as whole blood, red blood cells, plasma, platelets and leukocyte concentrates.
In an effort to alleviate this problem, it has been proposed to subject the blood products at the time of xe2x80x9cmanufacturexe2x80x9d to HTST heating similar to that practiced in sterilization and pasteurization processes to achieve substantially complete destruction of pathogens in the blood while maintaining cellular viability. The trouble is, that the HTST systems currently used in sterilization and pasteurization processes are not able to achieve the time-temperature relationship that produces a sufficient reduction of contaminating viruses while preserving biological activity in the blood products.
Also, the paper entitled High-Temperature Short-Time Heat Inactivation of HIV and Other Viruses In Human Blood Plasma, by S. E. Charm, et al., published in Vox Sang, 1992; 62:12-20, hereby incorporated by reference herein, discloses an HTST system specifically designed to inactivate HIV and other viruses in human blood plasma. However, the system described there is limited to heating only a 10 ml bolus of fluid. Still, the data obtained by the authors of that article are useful in establishing the feasibility of using microwave heating to deactivate viruses in blood plasma and indicate that a high-level of virus inactivation with modest to no changes in plasma components can be achieved with microwave exposure times of 0.006 second at a temperature between 75xc2x0 C. and 78xc2x0 C. With that temperature range, various viruses including HIV were reduced to less than the lowest detectable amount.
However, the prior HTST systems, including the one described in the above paper, are disadvantaged in that they are basically batch systems. Some take a relatively long time to reach the process temperature; some require a relatively long hold up time at the process temperature and some take a relatively long time to cool the process fluid to a non-destructive temperature. For example, one HTST system of which we are aware marketed by Alfa Laval under the name Sterimedia Mini and referred to in the above paper has a hold time of about 2 to 4 seconds or more and a hold up volume of 1.5 liters, making it necessary to waste a large volume of product during processing.
Accordingly, this invention aims to provide an improved method of inactivating viruses in blood products while maintaining cellular function.
Another object of the invention is to provide a method of inactivating viruses in blood products by high-temperature short-time heating of the blood products on a continuous in-line basis.
A further object of the invention is to provide an HTST heating method which overcomes limitations of the prior processes by delivering microwave heating to a well defined in-line flowing pathway of a blood product in a rapid, uniform and controlled manner.
Still another object of the invention is to provide a unique HTST heating technique that allows exposure of blood products to uniform microwave heating energy for the purpose of virus deactivation as the contaminated fluid flows in-line through a microwave heating chamber and then through a cooling chamber.
Yet another object of the invention is to provide a high-temperature short-time microwave heating method which permits the shaping of the heating time and temperature parameters to provide heat destruction of virus activity while maintaining the functional constituency of the otherwise heat-sensitive blood products.
A further object of the invention is to provide apparatus for heat treating blood products to achieve viral inactivation and having one or more of the above advantages.
Other objects will, in part, be obvious and will, in part, appear hereinafter.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying the features of construction, combination of elements and arrangement of parts which are adapted to effect such steps all as exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.
Briefly, our HTST system for achieving viral inactivation in blood products is an in-line system that processes the blood products on a continuous basis and in a rapid, uniform and closely controlled manner.
A blood product, e.g., whole blood, plasma, etc. is flowed through a series of at least two, and preferably three, coils, each of which has a small priming volume, e.g., 4-5 ml. The first coil is situated in a microwave heating chamber, the second coil reposes in a cooling chamber and the third coil (if present) is positioned in a second microwave heating chamber that may be similar to the first such chamber.
In the first coil, the blood product is exposed to uniform microwave energy present in the first chamber which heats the product to a temperature sufficient to deactivate any viruses present in the product. The heated product then flow through the second coil in the cooling chamber where it is immediately cooled to a lower delivery temperature.
Using non-invasive radiometric temperature sensors, the temperature profile along the product heating/cooling pathway is obtained and used to control the heating chamber to maintain a uniform product delivery temperature despite variations of fluid parameters such as flow rate and inlet temperature. In this way, the product heating time and temperature parameters may be controlled carefully to allow complete destruction of virus activity in the blood product while maintaining the viability of the product.
As noted above, in many cases it is desirable to route the blood product through a third coil positioned in a second microwave heating chamber. This allows the product to be cooled in the cooling chamber to a temperature below the desired delivery temperature and then be heated somewhat so that the target temperature is approached from below. This allows optimum control over the product delivery temperature.
Preferably, the coils are provided as single use disposable cartridges with conventional connectors at opposite ends of the tubing runs to enable the cartridges to be connected together and to the blood product source and destination. Alternatively, the two or three coils may be formed together as a single cartridge unit. The source and destination may be standard blood bags when processing stored blood products or cannulae if a patient""s blood is being processed extracorporally in a manner similar to dialysis.
The cartridges are designed to plug into receptacles in the heating and cooling chambers so that they are automatically positioned at the proper locations in those chambers as described in commonly owned U.S. Pat. No. 5,073,167 and pending application Ser. No. 08/142,577, the contents of which are hereby incorporated by reference herein.
For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing which is a schematic view of a treatment apparatus incorporating the invention.